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Offspring Number Versus Size• ___________________: If organisms use

energy for one function such as growth, the amount of energy available for other functions is reduced.– Leads to trade-offs between functions such as…

BIOL 3240 Plant and Animal Ecology – Life Histories

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Egg Size and Number in Fish• _____ show more variation in life-history than any

other group of animals.– Turner and Trexler found darter populations that

produce many small eggs showed less difference in allelic frequencies than populations producing fewer, larger eggs.• Proposed larvae from larger eggs hatch earlier, feed earlier,

do not drift as far, and thus do not disperse great distances.– Greater isolation leads to rapid gene differentiation.

BIOL 3240 Plant and Animal Ecology – Life Histories

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Seed Size and Number in Plants

• Many families produce small number of larger seeds.–

BIOL 3240 Plant and Animal Ecology – Life Histories

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Seed Size and Number in Plants

• Westoby et al. recognized four plant forms:– _______________: Grass and grass-like plants.– _______________: Herbaceous, non-graminoids.– _______________: Woody thickening of tissues.– _______________: Climbing plants and vines.• Woody plant and climbers produced 10x the mass of

seeds than either graminoids or forbs.

BIOL 3240 Plant and Animal Ecology – Life Histories

55

Seed Size and Number in Plants

• Westoby et al. recognized six seed dispersal strategies:– ___________: No specialized structures.– ___________: Hooks, spines, or barbs.– ___________: Wings, hair, (resistance structures).– ___________: Oil surface coating (elaisome).– ___________: Fleshy coating (aril).– ___________: Gathered, stored in caches.

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Seed Size and Number in Plants

• Small plants producing large number of small seeds appear to have an advantage in…

– Plants producing large seeds are constrained to producing fewer seedlings more capable of surviving environmental hazards.

BIOL 3240 Plant and Animal Ecology – Life Histories

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Seed Size and Number in Plants

• Jakobsson and Eriksson found seed size variation explained many differences in recruitment success.–

BIOL 3240 Plant and Animal Ecology – Life Histories

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Seed Size and Number in Plants

• Seiwa and Kikuzana found larger seeds produced taller seedlings.– Energy reserve boosts seedling growth.• Rapid growth helps seedling penetrate thick litter layer.

BIOL 3240 Plant and Animal Ecology – Life Histories

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Adult Survival and Reproductive Allocation

• Shine and Charnov pointed out vertebrate energy budgets are different before and after sexual maturity.– Before - – After - –

• Increased reproduction rate.

BIOL 3240 Plant and Animal Ecology – Life Histories

1010

Life History Variation Among Species• Gunderson found clear

relationship between adult fish mortality and age of reproductive maturity.– Species with higher

mortality show…

BIOL 3240 Plant and Animal Ecology – Life Histories

1111

Life History Variation Within Species

• Bertschy and Fox studied the influence of adult survival on pumpkinseed sunfish life histories.– Findings supported theory that when adult

survival is lower relative to juvenile survival, natural selection will…

BIOL 3240 Plant and Animal Ecology – Life Histories

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Life History Classification• MacArthur and Wilson– ______________(per capita rate of increase)• Characteristic high population growth rate.

– ______________(carrying capacity)• Characteristic efficient resource use.

• Pianka : r and K are ends of a continuum, while most organisms are in-between.– r selection: – K selection:

BIOL 3240 Plant and Animal Ecology – Life Histories

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r and K: Fundamental ContrastsBIOL 3240 Plant and Animal Ecology – Life Histories

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Plant Life Histories

• Grime proposed two most important variables exerting selective pressures in plants:– • Any process limiting plants by destroying biomass.

– • External constraints limiting rate of dry matter

production.

BIOL 3240 Plant and Animal Ecology – Life Histories

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Plant Life Histories

• Four Environmental Extremes:– Low Disturbance : Low Stress– Low Disturbance : High Stress– High Disturbance : Low Stress– High Disturbance : High Stress

BIOL 3240 Plant and Animal Ecology – Life Histories

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Plant Life Histories• ____________ (highly disturbed habitats)– Grow rapidly and produce seeds quickly.

• ____________ (high stress - no disturbance)– Grow slowly - conserve resources.

• ____________ (low disturbance low stress)– Grow well, but eventually compete with others for

resources.

BIOL 3240 Plant and Animal Ecology – Life Histories

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Plant Life HistoriesBIOL 3240 Plant and Animal Ecology – Life Histories

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Opportunistic, Equilibrium,and Periodic Life Histories

• Winemiller and Rose proposed new classification scheme based on age of reproductive maturity (α), juvenile survivorship (lx) and fecundity (mx).– Opportunistic: low lx – low mx – early α

– Equilibrium: high lx – low mx – late α

– Periodic: low lx – high mx – late α

BIOL 3240 Plant and Animal Ecology – Life Histories

1919

Opportunistic, Equilibrium,and Periodic Life Histories

BIOL 3240 Plant and Animal Ecology – Life Histories

2020

Reproductive Effort, Offspring Size, and Benefit-Cost Ratios

• Charnov developed a new approach to life history classification.– Took a few key life history features and converted

them to dimensionless numbers.• By removing the influences of time and size, similarities

and differences between groups are easier to identify.

BIOL 3240 Plant and Animal Ecology – Life Histories

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Reproductive Effort, Offspring Size, and Benefit-Cost Ratios

BIOL 3240 Plant and Animal Ecology – Life Histories

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Review

• Offspring Number Versus Size– Animals – Plants

• Adult Survival and Reproductive Allocation• Life History Classification– r - Selected– K - Selected– New Models

BIOL 3240 Plant and Animal Ecology – Life Histories